How to design a sail that won’t tear or melt on an interstellar voyage

Astronomers have been waiting decades for the launch of the James Webb Space Telescope, which promises to peer farther into space than ever before. But if humans want to actually reach our nearest stellar neighbor, they will need to wait quite a bit longer: a probe sent to Alpha Centauri with a rocket would need roughly 80,000 years to make the trip.

Artist rendering of the Starshot Lightsail spacecraft during acceleration by a ground-based laser array.
Artist rendering of the Starshot Lightsail spacecraft during acceleration by a ground-based laser array. Previous conceptions of lightsails have imagined them being passively pushed by light from the sun, but Starshot’s laser-based approach requires rethinking the sail’s shape and composition so it won’t melt or tear during acceleration. (Image: Masumi Shibata, courtesy of Breakthrough Initiatives)

Igor Bargatin, associate professor in the Department of Mechanical Engineering and Applied Mechanics, is trying to solve this futuristic problem with ideas taken from one of humanity’s oldest transportation technologies: the sail.

As part of the Breakthrough Starshot Initiative, he and his colleagues are designing the size, shape, and materials for a sail pushed not by wind, but by light.

Using nanoscopically thin materials and an array of powerful lasers, such a sail could carry a microchip-sized probe at a fifth of the speed of light, fast enough to make the trip to Alpha Centauri in roughly 20 years, rather than millennia.

“Reaching another star within our lifetimes is going to require relativistic speed, or something approaching the speed of light,” Bargatin says. “The idea of a light sail has been around for some time, but we’re just now figuring out how to make sure those designs survive the trip.”

Much of the earlier research in the field has presumed that the sun would passively provide all of the energy that light sails would need to get moving. However, Starshot’s plan to get its sails to relativistic speeds requires a much more focused source of energy. Once the sail is in orbit, a massive array of ground-based lasers would train their beams on it, providing a light intensity millions of times greater than the sun’s.

Bargatin, Deep Jariwala, assistant professor in the Department of Electrical and Systems Engineering, and co-authors have published a pair of papers in the journal Nano Letters that outline some of those fundamental specifications.

Read more at Penn Engineering Today.